This invention relates to a sheet feeding apparatus and more particularly to a paper feeding roller for feeding sheets of paper such as copy sheets or print-out sheets to a body in copiers or printing presses.
In conventional copiers, printing presses or the like, sheets of paper pre-cut into a given size are utilized as a final support such as copy sheets or print-out sheets, a paper-feeding roller is used to feed the sheets, sheet by sheet into the copier. Most paper-feed rollers of this kind utilize a frictional force generated in the peripheral surface of the rollers, but in a case where sheets come into intimate contact with one another, a piled-feed occurs in which a plurality of sheets are simultaneously fed. With W representing the pressure at which the paper-feed roller is pressed against a sheet, the aforementioned piled-feed will occur as a result of the fact that sheets of paper are brought into intimate contact with one another and the coefficient of friction in static frictional force F increases to provide the relationship of f &gt; F between the feed force f by the paper-feed roller and the static frictional force F.
Conversely, if the static frictional force F is greater than the feed force f, misfeed occurs and no sheet can be fed at all.
From the above, it is advisable to minimize the pressure force W of the paper-feed roller while increasing the feed force in order to carry out paper-feeding without occurrence of both piled feed and misfeed; however, in the paper-feed roller system it is impossible to not use the pressing force W at all, and therefore, in an ideal paper-feeding means the pressing force W is applied to the sheet only when necessary, and at the same time, speed of paper feed is increased to enhance the feed force f.
Accordingly, it is an object of this invention to provide a feed-roller system that increases the feed force while minimizing the pressing force on sheets to be fed by the feed-roller system.
Another object of the invention is to reduce the piled feed and misfeed of sheets due to an excessive pressing force.
Yet another object of this invention, is to increase the contact area of the paper-feed roller with sheets to be fed while simultaneously decreasing the pressure force on the sheets.